Electrophotographic process

ABSTRACT

In an electrophotographic process in which the electrostatic latent image on a photosensitive plate is developed by a liquid developer and the resulting toner image is transferred to a copying material, an electric field is applied to the liquid developer squeezing means in order to prevent the disturbance of the toner image caused by the flow of toner particles in a carrier pool formed at the squeezing site. The electric field is applied in such a direction that toner particles are attracted to the photosensitive plate before transferring the toner particles to the copying material and/or toner particles are attracted to the copying material after transferring the toner particles to the copy material.

United States Patent Takahashi [4 1 May 16,1972

Canon Camera Kabushiki Kaisha, Tokyo, Japan [22] Filed: May 16,1968

[21] Appl.No.: 729,567

[73] Assignee:

[30] Foreign Application Priority Data June 29, 1967 Japan ..42/56049 May 23, 1967 Japan ..42/32962 [52] US. Cl. ..96/l.4, 96/1 LY, 1 17/37 LE, 118/637, 355/10 [51] Int. Cl. ..G03g 13/22, 603g 13/10 [58] Field ofSearch .96/1, 1.4; 117/37 LX, 17.5; 118/637 [56] References Cited UNITED STATES PATENTS 3,128,683 4/1964 Rubin ..117/37 L X 3,147,679 9/1964 Schaffert.. .....96/1.4 X 3,155,546 11/1964 Dirks ..118/637 3,241,957 3/1966 Fansen et al ..96/1 3,332,396 7/1967 Gundlach 3,355,288 11/1967 Matkan 3,368,526 2/1968 Matsumoto et 211..

3,461,843 8/1969 Noon 3,147,679 9/1964 Schaffert 3,284,224 1 H1966 Lehmann... ...1 17/37 L X 3,419,411 12/1968 Wright ..ll7/37LX Primary Examiner-Charles E. Van Horn Attorney-Ward, McElhannon, Brooks and Fitzpatrick 571 ABSTRACT in an electrophotographic process in which the electrostatic latent image on a photosensitive plate is developed by a liquid developer and the resulting toner image is transferred to a copying material, an electric field is applied to the liquid developer squeezing means in order to prevent the disturbance of the toner image caused by the flow of toner particles in a carrier pool formed at the squeezing site. The electric field is applied in such a direction that toner particles are attracted to the photosensitive plate before transferring the toner particles to the copying material and/or toner particles are attracted to the copying material after transferring the toner particles to the copy material.

2 Claims, 5 Drawing Figures PATENTEDMAY 16 1912 SHEET 1 [1F 2 ELECTROPHOTOGRAPHIC PROCESS This invention relates to an electrophotographic process--, and more particularly, this invention relates to image reproduction by an electrophotographic process having liquid developing transfer and squeezing steps.

Electrophotography was invented by C.F. Carlson in 1938. The fundamental principle of C. F. Carlson's process is disclosed in US. Pat. Nos. 2,221,776, 2,297,691, and 2,357,809.

In general, C. F. Carlsons process comprises the following steps. Namely, a photosensitive plate prepared by laying a photoconductive insulating layer on a conductive base, is uniformly charged and image light is projected on the layer to form a latent image by selectively discharging the above obtained uniform charge, and thereafter the latent image is developed with toner particles of electrically opposite polarity.

The image of particles or powder is fixed directly with heat or with solvent, or is transferred onto another member.

Liquid developing methods for developing an electrostatic charge pattern with invented by Metcalfe et al. and are disclosed in US. Pat. Nos. 2,907,674 and 3,032,432. The photoconductive insulating layer retaining charge pattern is developed by contacting the same to a liquid developer through dipping or another method, and it is directly fixed, or transferred to other member.

In accordance with the conventional electrophotography there is a drawback that the image is disturbed when an electrostatic latent image is developed with liquid developer and the visible image thus formed is transferred onto copying material. Namely, when copying material is closely contacted to the surface of the developed visible image, most of the developing liquid remaining on the surface of the photosensitive plate is removed, and therefore an abrupt flow or pool of the developing liquid is brought about at portion where the close contact between the copying material and the photosensitive plate is started.

Therefore, the toner is dispersed or carried along with the flow of the liquid developer to cause the disturbance of the image.

Thus, in order to eliminate the disturbance of the image caused by the abrupt flow of the liquid developer, in accordance with one prior art method a predetermined gap is provided between the surface of the developed image and the copying material, an electric field is establish between the surface of the developed image and copying material.

However, this method has problems which are difficult to overcome from a technical point of view. In other words, a considerable amount of carrier liquid adheres on the copying material after the transfer of the image, in addition to the toner particles, and therefore it is necessary to remove the carrier liquid which adheres on the copying material.

A large amount of liquid developer is wasted if the carrier liquid is evaporated by directly drying the same with hot air by using a fan. Furthermore, there is a problem which is not preferably from the sanitary point of view because of the evaporated gas, and the energy required for drying the liquid developer is remarkably great, and such drawbacks as mentioned above are inherent in the conventional method.

In order to remove the above given drawbacks, another prior art method removes liquid developer on a copying material by passing the copying material through squeezing rollers before it is subjected to hot air drying treatment. However, when an ordinary paper is used as a copying material, the toner particles are carried along with the flow or the transfer of the liquid developer to disturb the image since there is no more electric attraction between the copying paper and the toner particles, which is a drawback of this method.

The present invention relates to a method according to which a photosensitive plate is uniformly charged, and then a light image is irradiated thereon, and then the obtained latent image is developed in accordance with liquid developing process, and the copying material is brought close to the photosensitive plate, and before or after the copying material is brought close to the photosensitive plate to transfer the developed image, an excessive amount of carrier liquid is squeezed, and in accordance with this invention the electric field in the direction in which the toner is pressed onto the photosensitive plate or copying material is given to the squeezing rollers, and it is possible thereby to prevent the disturbance of the toner image even if the carrier liquid should be squeezed out, and very excellent reproduced image can be obtained.

In other words, before the developed image is transferred,

an electric field is given to the liquid developer squeezing rollers in a direction that the toner is pressed onto the photosensitive plate.

After the developed image is transferred, an electric field is applied to the liquid developer squeezing rollers in a direction that the toner particles are electrically attracted onto the copying material.

The method for forming electrostatic latent image, which can be employed in this invention, is not restricted-only to the conventional electrostatic latent image forming methods, but the techniques which are disclosed in copending and commonly assigned U.S. Pat. application Ser. Nos. 563,899 and 571,538 may be employed.

It is therefore an object of this invention to provide a new electrophotographic copying process.

It is a further object of this invention to provide a process in which a liquid developing step for electrostatic latent image characterized by high speed and precise image property and a step for transferring the developed image to ordinary papers of low cost and easy handling a are advantageously combined without losing the advantages of both of them.

It is still a further object of this invention to provide a new and excellent process by applying an appropriate electric field to the liquid developer squeezing rollers before or after the image transfer process.

The above mentioned and other objects of this invention will be clarified from the descriptions in the following explanations, the claims and the attached drawings wherein:

FIG. 1 is diagram showing the process in which the liquid developer is squeezed before the toner image on the photosensitive plate is transferred;

FIG. 2 is a diagram showing an application of the liquid developer squeezing process of this invention as is shown in FIG. 1 to an electrophotographic copying device;

FIG. 3 shows the liquid developer squeezing process of this invention after the toner image is transferred;

FIG. 4 shows the side view of an electrophotographic copying device to which the liquid developer squeezing process of this invention is applied after the toner image is transferred; and

FIG. 5 shows the side view of another electrophotographic copying device to which the liquid developer squeezing process of this invention is applied after the toner image is transferred.

FIG. 1 shows the liquid developer squeezing process of this invention before the toner image is transferred. First, and electrostatic charge of a predetermined polarity is given to the photosensitive plate A having a photoconductive layer 2 on the support 1 in accordance with a conventional method, and then the light image of the original image is projected, and thereafter, the latent image is developed by a liquid developing process to form a toner image on the photosensitive member A. After development excessive amount of carrier liquid 3 remains on the photosensitive member A--. The toner image is transferred onto the copying material 4, and when the copying material 4 and the photosensitive member A having the toner 5 and the carrier liquid 3 closely contact each other, an electric field in the direction for pressing a toner 5 onto the photosensitive member A, is applied to the liquid developer squeezing roller 6.

Thus, the disturbance of the toner image can be prevented even if the carrier liquid 3 should be carried out when the photosensitive member A and the copying material 4 are closely contacted.

Thereafter, an electric field of polarity opposite to that of the electric charge of the toner is applied to the transferring roller 7 to have the toner 5 absorbed to the copying material 4 when the copying material 4 is separated from the photosensitive member A.

As the means for applying the electric field to the liquid developer squeezing roller 6 for squeezing out the liquid developer before the toner image is transferred and to the transfer-roller 7, a method may be employed, for example, wherein an electric field of the same polarity as that of the electrostatic charge of the toner 5 is applied to the squeezing roller 6 and an electric field of the opposite polarity to that of the toner 5 is applied to the transfer-roller 7 by means of the electric source 5,.

The means for applying the electric field is not restricted to the above methods. For example, one of the liquid developer squeezing rollers may be made of an insulating material and the liquid developer may be squeezed while corona a discharge is applied to the roller.

As an example of above, a copying material is faced to a negative toner image, and the two are closely contacted each other with the electroconductive rubber rollers 6 and 7 under a pressure of about I00 g/cm, and about '-1000 V of DC voltage is given to the roller 6, and about +1000 V of DC voltage is applied to the roller 7.

Thereby, no flow of image is observed at all, and the next copying operation can be performed at the copying efficiency of 100 percent without requiring a cleaning operation.

An excellent result is obtained when this invention is applied to the latent image produced by the processes and the photosensitive plates disclosed in U.S. Pat. application Ser.

Nos. 563,899 and 571,538.

The following is an explanation of the diagram of FIG. 2; FIG. 2 shows the combination of an electrophotographic copying device and the transfer-roller 7 and the liquid developer squeezing roller 6.

In this device, the photosensitive plate A is composed of a cylindrical drum which rotates continuously.

The photosensitive plate A comprising a photoconductive layer 2 on a support I is charged by means of corona discharger l0 Thereafter image light of the original copy is projected by using the exposing device 11 to form the electrostatic latent image on the photosensitive plate A. And the photosensitive plate is dipped into the liquid developer in a vessel 12 to develop the latent image.

After having developed the electrostatic latent image, the copying material 4 is introduced between the cylindrical photosensitive plate A and the transfer roller 7 and the liquid developer squeezing roller 6. When the copying material 4 is introduced between the photosensitive plate A and the transfer-roller 7, the liquid developer squeezing roller 6, a voltage of the same polarity as that of the electrostatic charge of the toner image formed on the cylindrical photosensitive plate A is applied to the liquid developer squeezing roller 6. On the other hand, a voltage of polarity opposite to that of the electrostatic charge of the toner image is applied to the transfer roller 7 to increase the image transferring effect.

When the polarity of the toner particles was adjusted to be negative and a DC voltage of about 1000 V was applied to the roller 6 and a DC voltage of about +1000 V was applied to the roller 7, image flow was not observed at all,--. Thereafter a drying operation was carried out by using the hot air drier 17 and an excellent image was obtained.

The following is an explanation about the diagram of FIG. 3; FIG. 3 shows a liquid developer squeezing roller for squeezing out the excessive carrier liquid remaining on the copying material after the toner image is transferred.

After the toner 5 is transferred onto the copying material 4, a considerable amount of carrier liquid 3 in addition to the toner 5 is adhered on the copying material 4.

In order to remove the carrier liquid 3, an electric field in a direction in which the toner 5 is electrically attracted to the copying material 4 developer squeezing rollers 8 and 9 are operated by any optional means, is applied between the liquid developer squeezing rollers 8 and 9 which are operated by any operational means (not shown). Thus, the disturbance of the image caused by the flow of the liquid developer can be prevented.

In regard to the means for applying the electric field, an electric field can be applied between the liquid developer squeezing rollers 8 and 9 by means of the electric source E; as is shown in FIG. 3. Of course the means for applying the electric field should not be restricted to the above. For example, one of the liquid developer squeezing rollers may be made of an insulating material and the liquid developer may be squeezed while a corona discharge is applied to the roller.

When an electric field is applied between the liquid developer squeezing rollers 8 and 9, it is necessary to provide at least one means for preventing the rollers 8 and 9 from contacting each other, or for covering either of said rollers 8 and 9 with electrically insulating material or semiconductive material in order to prevent the liquid developer squeezing rollers 8 and 9 from short-circuiting when the copying material 4 does not pass between the liquid developer squeezing rollers 8 and 9.

As is shown in FIG. 3 it is possible to insert a resistance R to the voltage applying circuit.

When the copying material 4 is passed between the squeezing rollers 8 and 9, a voltage from 50 V to 3 kv is applied between the rollers 8 and 9 in such a direction that the toner 5 is electrically attracted to the copying material 4. Thus, the toner particles 5 can be attracted to the copying material 4 by the electric field when the carrier liquid 3 adhered on the copying material is removed by the squeezing rollers.

Therefore, it is possible to produce excellent transferred image without causing the disturbance of the image. It is not an indispensable factor of this invention that two liquid developer squeezing rollers 8 and 9 should be provided, rather it is quite possible to replace either of the squeezing rollers by other additional means for squeezing the liquid developer. For example, one of the liquid developer squeezing rollers 8 and 9 may be replaced by a squeezing means other than a roller.

The following is an explanation of FIG. 4 which shows an embodiment of a electrophotographic device in which the squeezing rollers 8 and 9 shown in FIG. 3 are combined.

In this device, the photosensitive plate A is composed of cylindrical drum which, in operation, rotates continuously.

First, the photosensitive plate A comprising a photo-conductive layer 2 on a support 1 is charged by means of the corona discharger l0, and then the image light of the original copy is projected by means of the exposing means 11 to form electrostatic latent image on the photosensitive plage A. Then, the photosensitive plate is dipped in the liquid developer to develop the latent image. Thereafter, the copying material 4 is laid thereon with a slight distance from the surface of the image.

An electric field is applied through the electroconductive roller 7 for image transfer from the back surface of the copying material 4 and the developed visible image is transferred to the copying material 4 by making use of the electrophoresis of the toner particles 5 contained in the liquid developer.

After the completion of the image transfer, the copying material 4 is passed through the squeezing rollers 8 and 9 in order to remove a considerable amount of the carrier liquid 4 adhered on the copying material 4.

When the copying material 4 is passed through the squeezing rollers, a voltage is applied between the two squeezing rollers 8 and 9 by means of the electric source E in the direction in which the toner particles 5 are electrically attracted to the copying material 4.

In other words, when the toner particles 5 are negative, a negative voltage is supplied to the squeezing roller 8, and a positive voltage is supplied to the squeezing roller 9.

When a voltage from 50 V to 3 kv is applied between the squeezing rollers 8 and 9, the toner particles 5 are attracted to the copying material 4 by means of the electric field and the carrier liquid 3 adhered on the copying material 4 is removed.

Therefore, after having dried the same with a hot air drier 17, an excellent image can be obtained without disturbing the image.

After having transferred the toner image, the photosensitive plate A is cleaned with the cleaning brush and the copying operation can be carried out over again.

It is not an indispensable factor of this invention that two liquid developer squeezing rollers 8 and 9 be provided, but rather either of them can be replaced by other additional means for squeezing off the liquid developer. For example, one of the liquid developer squeezing rollers 8 and 9 may be replaced by a squeezing means other than a roller.

The following is an explanation about FIG. 5 which shows a modified electrophotographic copying device of the type shown in FIG. 4.

The modified electrophotographic copying device of FIG. 5 is the same as the electrophotographic device of FIG. 4 except that the image transferring roller 7 also works as the squeezing roller 9 in the electrophotographic device.

In the device of FIG. 5 the photosensitive plate A is composed of a continuously rotating cylindrical drum, and the photosensitive plate A comprising a photoconductive layer 2 on a support 1 is charged by means of a corona discharger 10, and then the light image of the original copy is projected by using the exposing means 11 and an electrostatic latent image is formed on the photosensitive plate A.

Thereafter, the photosensitive plate is dipped into the developer liquid contained in the vessel 12 to develop the latent image and copying material 4 is laid thereon with a slight distance from the surface of the image.

An electric field is applied from the back surface of the copying material 4 through an image transferring electroconductive roller 7 which functions as a transferring and squeezing roller, and the visible image is transferred onto the copying material 4 by making use of the electrophoresis of the toner particles 5 contained in the liquid developer.

After having transferred the image, in order to remove the carrier liquid 3 adhered on the copying material 4 in a considerable amount, the copying material 4 is passed through the squeezing rollers 8 and the transferring roller 7.

When the copying material 4 is passed between the squeezing rollers, a voltage is applied to the squeezing roller 8 by means of the electric source E in a direction in which the toner particles 5 are electrically attracted to the copying material 4.

When a voltage from 500 V to 3 kv is applied between the squeezing roller 8 and the image transferring roller 7, the toner particles 5 are attracted by an electric field to the copying material 4 and the carrier liquid 3 which is adhered on the copying material 4 is removed, and therefore it is possible to produce an excellent image without disturbing the image.

After the completion of the transfer of the toner image the photosensitive plate A is cleaned by the cleaning brush 15, and the copying operation can be carried out repeatedly.

As is shown in FIG. 3, FIG. 4 and FIG. 5, it is preferable that the copying material 4 should be kept almost horizontal in order to prevent the disturbance of image caused by the flowing out of the carrier liquid at the region between the transferring roller 7 and the squeezing rollers 8 and 9.

As has been explained so far, this invention provides a new and remarkably effective electrophotographic process having a liquid developer squeezing step free from any disturbance of image which is caused by the flowing out of the liquid developer when the liquid developer is squeezed with the conventional liquid developer squeezing rollers.

According to a conventional process the transferred image is disturbed upon transferring the image on the photosensitive plate to the copying material by closely contacting the copying material to the image. This invention eliminates such disadvantage by squeezing the liquid developer before the transfer under application of electric field to the squeezing roller.

Further, according to a conventional process, the transferred image is disturbed when the image on the photosensitive plate is transferred to the copying material by closing the image on the photosensitive plate to the copying material and then the liquid developer is squeezed by the liquid developer squeezing roller. This invention succeeds in removing such disadvantage by squeezing the liquid developer after imagetransfer under application of an appropriate electric field to the liquid developer roller.

In accordance with this invention, there is an advantage that the liquid developer can be effectively used by re-using the carrier liquid removed from the copying material by returning the same through the guide path (not shown) into a storage tank.

On the other hand, in accordance with this invention, it is possible to use ordinary paper as the copying material, and the cost of the copying material is low.

The structure of the squeezing device in accordance with the liquid developer squeezing process of this invention is very simple and can be produced economically.

It is possible to squeeze out the liquid developer at a high speed when the liquid developer squeezing process is employed, and therefore this invention is very useful in the electrophotographic copying devices in which liquid developing process is adopted.

The above are the explanations about the concrete embodiments given for explaining this invention, but it will be appreciated by those skilled in the art that this invention includes various kinds of modifications and the varieties within the scope of this invention as is described in the claim of this invention.

What is claimed is:

1. An electrophotographic process comprising the steps of forming an electrostatic latent image on an electrophotographic photosensitive member, developing the electrostatic latent image with a liquid developer containing a liquid carrier and a charged toner to form a toner image on said photosensitive member, squeezing said photosensitive member, liquid carrier, charged toner and copying material between a first rotatable electroconductive roller and a support member for squeezing out excessive amounts of liquid carrier while applying a potential of the same polarity as that of said charged toner to cause said charged toner to adhere to said photosensitive member, and then applying a potential of opposite polarity while the photosensitive sheet, toner image and copying material are held between a second rotatable electroconductive roller and a support member to effect transfer of said toner image to said copying material. 1

2. An electrophotographic process for reproducing an original image on copying material comprising the steps of forming an electrostatic latent image of said original image on an electrophotographic photosensitive member, developing said electrostatic latent image with a liquid developer containing a liquid carrier and charged toner to form a toner image on said photosensitive member, contacting said toner image with said copying material and squeezing said photosensitive member and said copying material to remove excessive amounts of liquid carrier while applying an electric field which adheres said charged toner to the surface of said photosensitive member, and, thereafter, transferring said toner image to said copying material by contacting said copying material with said photosensitive member while applying an electric field which attracts the toner image to the surface of said copying material. 

2. An electrophotographic process for reproducing an original image on copying material comprising the steps of forming an electrostatic latent image of said original image on an electrophotographic photosensitive member, developing said electrostatic latent image with a liquid developer containing a liquid carrier and charged toner to form a toner image on said photosensitive member, contacting said toner image with said copying material and squeezing said photosensitive member and said copying material to remove excessive amounts of liquid carrier while applying an electric field which adheres said charged toner to the surface of said photosensitive member, and, thereafter, transferring said toner image to said copying material by contacting said copying material with said photosensitive member while applying an electric field which attracts the toner image to the surface of said copying material. 